The 85-year-old Arpaio could shake up the late August Republican primary in a critical open-seat race to replace retiring Sen. Jeff Flake, R-Ariz. Trump pardoned Arpaio last summer, sparing the former sheriff jail time after he was convicted of ignoring a federal court order in a racial-profiling case.

The polarizing yet iconic former Maricopa County sheriff, beloved by many conservatives for his hawkish immigration policies, presents an alternative to the unimpressive Kelli Ward and a potential obstacle to Rep. Martha McSally. She is expected to launch within days and is widely viewed as the Republicans' strongest general election candidate.

In a telephone interview with the Washington Examiner, Arpaio shrugged off concerns about his age, dismissed Republican insiders' anxiety that his poor reputation with nonwhite voters would put the seat in play for the Democrats in the midterm, and discussed plans to work with Trump on behalf of Arizona.